Study finds link between fish oil and higher prostate cancer risk

A new study is raising questions about omega-3 fatty acids, which are found in oily fish and fish supplements, suggesting that men with high levels of the oils in their bloods might also have a higher risk of prostate cancer.

Omega-3 fatty acids have long been hailed for their apparent ability to lower blood pressure and cholesterol and perhaps protect against heart disease. They’ve also thought to have anti-inflammatory properties that might help prevent a number of forms of cancer.

But a new study has found that men with prostate cancer were more likely to have higher levels of omega-3 fatty acids in their blood than similar men without prostate cancer.

Of the 834 men studied, those with high levels of EPA, DPA and DHA omega-3 fatty acids were at 43 per cent greater risk of prostate cancer than those with low concentrations.

Those with the very highest levels of omega-3s also were 71 per cent more likely to have aggressive, "high-grade" prostate tumours than those with lower levels.

High levels of omega-3s equal a little more than two servings of salmon per week.

It is unclear why high levels of omega-3 fatty acids might be linked to a higher risk of prostate cancer risk. But the authors note that this study replicates similar findings they made in 2011, in a study that found a link between high blood levels of DHA and high-grade prostate cancer.

The authors say the reasons why omega-3s might be linked to prostate cancer aren’t clear. It's possible, they say, that fatty acids convert into compounds that can damage cells and DNA, or could suppress the immune system.

But it’s important to note that the study did not show a cause-and-effect relationship between omega-3s and cancer; it only drew a link between the two. It’s thus possible that there are other factors at play that could be affecting the risk of prostate cancer, such as genetics.

Prostate cancer patient Derek Lawrence, 82, says he takes a teaspoon of fish oil every morning and feels it is beneficial to his health.

“Sometimes you don’t get the whole story and people jump to conclusions,” Lawrence said, adding that he despite hearing about the study, he was not going to stop taking fish oil.

As well, the study looked only at blood levels of fatty acids and did not assess the participants’ diet or supplement use.

Canadian urologist Dr. Arthur Grabowski notes that the results of other studies on fish oil and prostate cancer conflict with the findings of this study.

Fish oil has been found to cut the risk of dying of prostate cancer by 40 per cent, and prevent heart disease and strokes.

"This is not the final word on whether omega 3 fatty acids put patients at higher risk for prostate cancer," he told CTV News.

"What I tell my patients is I recommend against taking any supplement to reduce the risk for any disease because there can often be unintended consequences to these supplements that we have not yet studied."

While Grabowski does not recommend his patients take omega-3 supplements, he does recommend they eat a healthy and balanced diet.

"Because a diet that has been shown to be healthy for your heart, in most cases, have been shown to be healthy for your prostate," he said.

VP research Prostate Cancer Canada Stewart Edmonds said people should be cautious about taking supplements.

“While they may be beneficial for other disease, they may risk other health problems,” Edmonds said.

The study used data from men who participated in the Selenium and Vitamin E Cancer Prevention Trial (SELECT), a large trial that looked at test whether selenium and vitamin E, might reduce prostate cancer risk. In fact, that study showed no benefit from selenium and an increase in prostate cancers in men taking vitamin E.

The researchers narrowed in on 834 men with prostate cancers, including 156 with high-grade cancer, and compared them to 1,393 men selected randomly from the 35,500 participants in SELECT.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip